support @DirtiesContext in context hierarchy

This commit improves @DirtiesContext to take parent context name in
context hierarchy. When parent context is specified, all child contexts
will be removed from the context cache after method/class.

- Allow @DirtiesContext to specify parent context name
- Introduced 'name' in MergedContextConfiguration which holds the name
  from @ContextConfiguration
- Unit tests

Issue: SPR-5613